It is generally known that a good holding device can be the key element to the quality of a machining process. However, for the modern small-volume large-variety production of custom-made products, the cost for designing holding devices for a wide range of different items can be a huge burden in any case. In addition to the need for developing a specifically designed holding device for each product, the mounting and detaching of such specifically designed holding device can be very complicated that the production line may not be flexible enough for allowing the same to be converted rapidly for producing another products. Moreover, in the processes for producing large parts for ships, aircrafts or automobiles, the number of holding devices that are required in the production process can be huge, resulting that not only the production cost can be colossal, but also there may require a huge space just for storing such tremendous amount of holding devices.
Conventionally, most support devices available today are designed as a universal joint with suction cups for adapting the same passively to the curves of a workpiece. Nevertheless, since the aforesaid conventional passive holding means is substantially a free support structure, the suction cups can be forced to displace freely when the workpiece is under pressure, and further can be deformed by the process working on the workpiece so that the suction cups may not be able to attached themselves effectively on the workpiece conforming to the curves of the workpiece for fixedly holding the same. Moreover, although the conventional suction cups are generally being assisted by a vacuuming means for reinforcing their ability to attach themselves upon a workpiece, the attachment may not be stably achieved on a workpiece surface with a large inclination angle that exceeds the maximum rotation angle of the universal joint. In addition, the universal joint may be rotated to an angle that obstructs the vacuuming of the suction cups, and thus the vacuum suction cups can not function normally.